The present invention relates to a process and die unit for fabricating stepped nails, wherein the stepped nails are designed for use in holding separate wooden pieces together.
To fasten wooden pieces together, nails are commonly used. However, the problem encountered is that a driven nail often causes a crack in the pieces, with the crack being due to the fact that the pointed portion of the nail radially wedges into the wooden pieces against the shearing strength thereof.
There have been a number of proposals to prevent wooden pieces from cracking when fastened together by nails, with such proposals including, for example, providing a nail having a slender tip portion with a diameter smaller than a diameter of a shank portion whereby the tip portion is clearly distinct from the shank portion by a shoulder.
Nails of this type are fabricated by cutting or pressing, but the cutting process is expensive, and is not suitable for mass production. The pressing involves a technical difficulty in forming a straight shoulder perpendicular to the axis of the shank portion, which is essential for nails to anchor in the wooden pieces.
An object of the present invention is to provide a process and a die unit which solve the problems pointed out above. Thus, an object of the present invention is to provide a process and a die unit for fabricating stepped nails easily and ecnomonically.
According to one advantageous aspect of the present invention, there is provided a process for fabricating stepped nails, with the process comprising pressing a top portion of a blank by a first die unit to shape the same into a rough slender tip portion, with the slender tip portion having a smaller diameter than the diameter of a shank portion of the blank, pressing the shank portion of the blank by a thread rolling die section of a second die unit so as to cut threads on the peripheral surface thereof, and simultaneously pressing the rough slender tip portion by a correction die section of the second die unit to refine the same into a finished slender tip portion.
According to another advantageous aspect of the present invention, there is provided a die unit for fabricating stepped nails, wherein the unit comprises a first die unit for pressing a top portion of a blank to shape the same into a rough slender tip portion, and a second die unit including a thread rolling die section for pressing a shank portion of the blank to cut threads on the peripheral surface thereof, and a correction die section for finishing the rough slender tip portion into a refined state.
Other objects and advantages of the present invention will become more apparent from the following detailed description, when taken in connection with the accompanying drawings which show, for the purposes of illustration only, one embodiment in accordance with the present invention .